HYDROGEOLOGY - Joseph H. Huemann & Sons Well Drilling, Pump Sales and Service, with its century old hydrogeologic cycle know-how, understands the geologic science behind the process of finding water sources deep in the earth’s surface. Well drilling is not about digging holes. It’s about understanding the subsurface of the earth and choreographing access to the aquifirs where groundwater lies.

Understanding Groundwater in the Great Lakes RegionGroundwater is a major natural resource in the Great Lakes Region that helps link the Great Lakes and their watershed. The Great Lakes water-resources issues can really only be addressed if this is fully understood.

The Great Lakes constitute the largest concentration of unfrozen fresh surface water in the western hemisphere–about 5,440 mi3. Because the quantity of water in the lakes is so large, groundwater in the Great Lakes Basin is often overlooked when evaluating the hydrology of the region. Groundwater is essential to the hydrology of the Great Lakes and to the health of its ecosystem. Groundwater is, in effect, a large, subsurface reservoir from which water is released slowly to provide a reliable minimum level of water flow to streams, lakes, and wetlands.

What are the major groundwater issues on the Great lakes Region?The major groundwater resources issues in the Great Lakes Region revolve around 1) the quantity of groundwater, 2) groundwater and surface-water interaction, 3) changes in groundwater quality as development expands, and 4) ecosystem health in relation to quantity and quality of water.

Love those Lakes!A major attraction of the Great Lakes Region is the abundant water supply on which manufacturing, power generation, transportation, agricultural, and recreational sectors have historically relied. Groundwater predominantly feeds surface water. Most large public water supplies are obtained from the lakes themselves, but groundwater is the source of drinking water for about 8.2 million people within the watershed. Although most residents of Chicago use water from Lake Michigan, many people in the Chicago suburbs who live outside of the watershed, but are close to it, use groundwater as a source of supply.

As the suburban areas near the watershed boundary expand, more and more people depend on groundwater to supply household water needs. Small manufacturing companies in suburban locations also are increasing their groundwater use. As communities encroach upon agricultural areas, conflicts between agricultural and other groundwater users will increase (Alley and others, 1999). Therefore, groundwater resources need to be characterized according to their occurrence, availability, quality, and use to develop a sustainable supply for all uses. Pumping groundwater can capture water from or intercept flow to streams and alter the area that contributes groundwater to the Great Lakes. Thus, groundwater withdrawals can divert groundwater that would normally discharge to the Great Lakes system.

In addition to water quantity issues in the Great Lakes Region, water quality also can be of concern. As development increases, activities that could threaten the quality of groundwater also increase. Human health needs to be safeguarded, as does the health of many other organisms that rely on clean water.

Geology and History establishes the framework for aquifersGroundwater is present throughout the Great Lakes Basin, but the quantity that can be withdrawn varies depending on the characteristics of the water-bearing rocks and sediments (aquifers). Material that was deposited at or near the land surface as a result of large-scale glacial ice advances and retreats during the last 2 million years make up the most productive aquifers. These deposits are as much as 1,200 feet thick in parts of Michigan and are several hundred feet thick in buried bedrock valleys in Illinois, Wisconsin, and New York.

The deposits are thin or nonexistent in areas where bedrock that was not easily eroded by glacial ice is exposed at land surface. Most glacial deposits are composed of mixtures of sand and gravel, and silt and clay. Sand and gravel deposits (outwash and ice-contact deposits) are the most productive aquifers because they have greater permeability and effective porosity than do the finer grained deposits. Some areas with silt and clay at the surface (till or glacial lake deposits) contain more permeable deposits at depth and are able to yield moderate to large amounts of water to wells. In general, however, the silt and clay deposits are not aquifers.

Bedrock aquifers are generally widespread throughout the region and are more continuous than the aquifers in glacial deposits. Carbonate rocks (limestone and dolomite) are the most common bedrock aquifers in the region. Natural processes may increase permeability by dissolving carbonate minerals in these aquifers, but this increased permeability makes the aquifers more vulnerable to contamination. The most extensive carbonate aquifer in the region consists of a series of limestones and dolomites that underlie a large part of the upper Midwest. Sandstone aquifers are the next most common bedrock aquifer. An extensive sandstone aquifer underlies much of the northern Midwest and even extends under Lake Michigan. In general, shale, and igneous and metamorphic bedrock have limited water-yielding capacity, and they are not considered regional aquifers.

How does groundwater move in the Great Lakes Region?Aquifers and confining units (relatively impermeable rocks and sediments) make up the groundwater system in the Great Lakes watershed. Recharge takes place between streams in areas that occupy most of the land surface. Groundwater moves in both local and regional flow systems.

Most groundwater moves in local flow systems Groundwater in local flow systems commonly travels relatively short distances underground before discharging to a stream, lake, or wetland. The Great Lakes Region has an abundance of small streams, and most groundwater flow takes place in these shallow systems. The most productive shallow aquifers are composed of sand and gravel.